Multiple sampling PSC-PWM with hierarchical control architecture for MMC-DSTATCOM

The modular multilevel converter (MMC) is attractive for medium- and high-power applications because of its high modularity, availability and power quality. In this study, a quadruple sampling phase-shifted-carrier pulse-width modulation (PSC-PWM) strategy based on hierarchical distributed control architecture for MMC in medium-voltage power distribution static synchronous compensator (DSTATCOM) application is presented. Compared to centralised control architecture, the multi-digital signal processors master-slave hierarchical control architecture can enhance the scalability of MMC-DSTATCOM and the sub-module (SM) number can expand without limitation. To take advantage of the proposed hierarchical architecture, the multiple sampling PSC-PWM technique is employed to improve the converter performance. The spectrum of the electromotive force of MMC with quadruple sampling is almost the same as that of natural sampling, which leads to fewer harmonics in reactive and harmonic current compensating. Besides, it also raises the sampling frequency so that the MMC-DSTATCOM can compensate harmonic at the low SM switching frequency. The effectivenesses of the proposed architecture and modulation method are verified by experimental results obtained from a 60 V/2 kVA downscaled prototype.